Supermarkets now sell us 97% of our groceries. As the big four continue to grow, small and independent competitors are in steady decline.

This week Ed Miliband backed a stronger voice for local people who oppose the spread of supermarkets in their towns. But the issue is not simple: supermarkets also offer jobs, convenient shopping and low-priced food. But have they become too powerful ... and if so, what can be done about it?